Smokeless manufacture of nickel-magnesium alloys

ABSTRACT

NICKEL MAGNESIUM ALLOYS ARE PRODUCED WITH NEGLIGIBLE PRODUCTION OF MAGNESIUM OXIDE SMOKE BY INTRODUCING PARTICULATE NICKEL INTO MOLTEN MAGNESIUM AT A TEMPERATURE ONLY SLIGHTLY ABOVE THE MELTING POINT OF MAGNESIUM AND THEN INTRODUCING THE RESULTING ALLOY INTO A BATH OF MOLTEN NICKEL.

United States Patent Oflice 3,552,951 SMOKELESS MANUFACTURE OF NICKEL- MAGNESIUM ALLOYS Robert D. Schelleng, Ramapo, N.Y., assignor to The International Nickel Company, Inc., New York, N.Y., a corporation of Delaware No Drawing. Filed Dec. 27, 1968, Ser. No. 787,548 Int. Cl. C22c 19/00 U.S. Cl. 75-170 5 Claims ABSTRACT OF THE DISCLOSURE Nickel magnesium alloys are produced with negligible production of magnesium oxide smoke by introducing particulate nickel into molten magnesium at a temperature only slightly above the melting point of magnesium and then introducing the resulting alloy into a bath of molten nickel.

In the production of ductile iron, i.e., magnesium-containing cast iron, the manner in which magnesium is introduced into molten cast iron has always been a matter of concern. A principal contributing reason for this has to do with the fact that magnesium not only melts at a low temperature, i.e., 650 C. (1202 F.), but also boils at a relatively low temperature, i.e., 1117 C. (2042 F.). The boiling temperature of magnesium is below the temperature at which molten cast iron baths must be held prior to casting. Thus, the addition of pure magnesium to molten cast iron is attended by a violent pyrotechnic display. As a result, magnesium is usually added to molten cast iron in the form of an alloy with another metal or metals.

Alloys which have been successfully employed for the purpose of introducing magnesium into molten cast iron in the production of ductile iron include nickel-magnesium alloys which can contain about 5% to about 25% of magnesium, up to about 4% of carbon and the balance essentially nickel. These alloys have survived competition from cheaper magnesium-containing alloys over a period of 20 years or more for the reason that these alloys provide good control in magnesium introduction, thereby reducing the likelihood of lost heats. The nickelmagnesium alloys have been produced in the past by melting nickel with carbon, e.g., about 2% of carbon, adjusting the temperature of the molten bath to be about 2425 F. and then adding the required magnesium to the melt either by thrusting magnesium ingots into the molten nickel-carbon bath or by pouring the molten bath over magnesium ingots held in a ladle. In either event, the process was accompanied by considerable vaporization of magnesium and with the production of clouds of smoke sufiicient in volume and density to cause complaints under relevant air pollution codes. Because of the severity of the air pollution problem, a method for producing nickel magnesium alloys which would avoid the production of magnesium oxide smoke is greatly to be desired.

Among the objects of the present invention is the production of nickel-magnesium alloys while mitigating or substantially completely avoiding the production of magnesium oxide smoke.

Broadly stated, the present invention is directed to a process for the production of nickel-magnesium alloys with high recovery of magnesium and minimal production of magnesium oxide smoke, which comprises reacting molten magnesium with particulate nickel, preferably in the form of reduced nickel oxide containing at least about 90% nickel, by weight, to form a molten alloy containing about 20% up to about 50% nickel with a balance essentially magnesium, while maintaining the bath 3,552,951 Patented Jan. 5, 1971 temperature at not more than about 300 F. in excess of the melting point of magnesium and thereafter introducing the resulting alloy into a molten nickel-carbon bath at as low a temperature as possible, e.g., about 2425 F., to provide a nickel-magnesium alloy contain ing about 5% to about 25% magnesium.

The preferred form of nickel for reacting with the molten magnesium bath is hydrogen-reduced high temperature nickel oxide granules produced initially by the roasting of granulated nickel sulfide at a temperature above the melting point of nickel sulfide, since a high rate of solution in molten magnesium is achieved at a low bath temperature through the use of this material. The initial nickel oxide material is described in US. Pat. No. 3,094,409 and the procedure for reducing the oxide material to a particulate nickel material containing at least about nickel is described in copending U.S. patent application Ser. No. 616,800 filed Feb. 17, 1967. It is found that when the preferred reduced nickel oxide material is employed, the reaction between molten magnesium and the particulate nickel material can be completed with the production of a nickel-magnesium alloy containing at least about 20% up to about 50% magnesium at bath temperatures in the range of about 1300 F. to 1500 F., i.e., at bath temperatures not exceeding the melting point of magnesium by more than about 300 F. On the other hand, when commercial nickel powder, such as carbonyl nickel powder, is added to the molten magnesium bath, it is found that a higher bath temperature on the order of about 1700 F. is required to dissolve the nickel. This is undesirable since magnesium losses increase as the temperature is increased. Furthermore, the attempts to produce the nickel-magnesium pre-alloy by reacting massive forms of nickel such as electroyltic nickel sheared squares and nickel shot, were unsuccessful since such forms of nickel only partially dissolve in the molten magnesium even when the bath temperature is increased to as much as l=800 F.

The addition of the nickel-magnesium pre-alloy result ing from the first step of the process to the molten bath of nickel containing carbon for purposes of reducing the melting point, e.g., about 1.3% to about 4% carbon, may be conducted in a number of ways. Thus, the pre-alloy can be cast into cakes of fixed dimension and weight and broken up for addition to the molten nickel-carbon bath. Alternatively, the initial nickel-magnesium bath may be transferred to the molten nickel bath in the molten condition with favorable eifects in terms of heat conservation and reduction in the length of time required to dissolve the initial nickel-magnesium material in the molten nickel.

In the production of the initial nickel-magnesium alloy bath, it is desirable to maintain a magnesium-type flux over the surface of the magnesium bath. A flux composed of equal parts of anhydrous magnesium chloride and calcium chloride fluidized with a small amount of sodium chloride is satisfactory.

In order to give those skilled in the art an illustration of the advantages of the invention, the following example is given. A charge comprising 500 parts by weight of magnesium was melted in a clay-graphite crucible in a gas fired furnace. After the magnesium was melted, a flux composed of equal parts of anhydrous magnesium chloride and calcium chloride fluidized with sodium chloride was added to the bath surface. The flux was added in amount sufficient to cover the surface of the magnesium but was not more than about A inch thick. The bath was heated to about 1300 F., and 500 parts byweight of particulate hydrogen-reduced high temperature nickel oxide containing about by weight, of nickel was added to the bath and stirred in. The temperature of the bath rose to about 1400 F. during the addition of the nickelcontaining material, but no fuming or burning occurred. The temperature rise was attributed to a Thermit reaction between magnesium and remaining oxygen in the nickel material. The resulting alloy contained about 50.3% nickel, was solidified and broken to sizes convenient for weighing. A second melt consisting of about 1800 parts by weight of electrolytic nickel, and 50 parts by weight of graphite was prepared in air induction furnace. The charge was heated to about 2850 F. to dissolve the graphite and was then cooled to a temperature reported by an immersion thermocouple as being about 2300 F. 800 parts by weight of the nickel-magnesium alloy previously produced was then added to the bath and stirred in. Only a negligible amount of fuming and burning of the magnesium occurred. The resulting alloy contained 13.55% magnesium.

The procedure employed in the foregoing example wherein a pre-alloy containing about 50% magnesium and about 50% nickel is used for addition to the molten nickel bath to provide the final nickel-magnesium alloy enables carrying out the overall process with only negligible quantities of magnesium oxide smoke being produced, if any. The process can also be conducted to yield a prealloy containing only about 20% to about 30% nickel with the balance essentially magnesium. When this procedure is used, the magnesium bath temperature need not exceed about 1300 F., the use of magnesium-type flux can be eliminated and the melt time can be shortened. In addition, a smaller quantity of material is added to the nickel bath in the production of the final nickel-mag nesium alloy, and hence the melt time for this portion of the process is shortened also. However, more smoke is evolved upon addition of the pre-alloy to the molten nickel bath although such smoke evolution is still much less than is the case when pure magnesium is added to the nickel bath. Of course, nickel-magnesium pre-alloys containing 30% to 50% nickel can be used as aforedescribed.

It is to be understood that the particulate nickel oxide material roasted at high temperature as described in US. Pat. No. 3,094,409 is usually of a particle size such that about 90% of the material will pass a 100-mesh screen but only about 2% of the material will pass a ZOO-mesh screen. This oxide material is essentially unreactive in contact with molten magnesium at about 1400 F. for reasons which are not thoroughly understood. However, when the particulate oxide material is reduced to the extent that it is about 90% to about.95% nickel, for example, by means of hydrogen at temperatures of about 750 F. to about 1100 F. as described in co-pending US. application Ser. No. 616,800, the resulting particulate metallic material is readily soluble in molten magnesium at temperatures of about 1300 F. to about 1400 F.

Although the present invention has been described in conjunction with preferred embodiments, it is to be understood that modifications and variations may be resorted to without departing from the spirit and scope of the invention as those skilled in the art will readily understand. lSUCh. modifications and variations are considered to be within the purview and scope of the invention and appended claims.

We claim:

1. A process for producing a nickel-magnesium alloy with high recovery of magnesium and minimal production of magnesium oxide smoke which comprises reacting molten magnesium with particulate reduced nickel oxide containing at least about 90% nickel, by weight, to form a molten alloy containing about 20% to about nickel with the balance essentially magnesium while maintaining the bath temperature at not more than about 300 F. in excess of the melting point of magnesium and thereafter introducing the resulting alloy into a molten nickelcarbon bath having a temperature not exceeding about 2425 F. to provide a nickel-magnesium alloy containing about 5% to about 25% magnesium.

2. The process according to claim 1 wherein the molten nickel-carbon bath contains about 1.3% to about 4% carbon.

3. The process according to claim 1 wherein the molten nickel-magnesium alloy is poured into the molten nickelcarbon bath.

4. The process according to claim 1 wherein the molten nickel-magnesium alloy is solidified and a portion of the solidified alloy is thereafter introduced into the molten nickel-carbon bath.

5. The process according to claim 1 wherein the reduced nickel oxide contains about 95% nickel, by weight.

References Cited UNITED STATES PATENTS 1,059,709 4/1913 Byrnes -135X 2,437,097 3/1948 King 75-134X 3,403,997 10/1968 Badia 75-170X Re. 26,042 6/1966 Grebe 75135X FOREIGN PATENTS 384,291 2/ 1931 Great Britain 75l70) L. DEWAYNE RUTLEDGE, Primary Examiner J. E. LEGRU, Assistant Examiner US. 01. X.R. 7s 134, 135, 168 

